Lotus Elan

Welded front crossmember

PostPost by: benymazz » Fri Nov 01, 2019 4:18 pm

All,

As anyone that has needed to drop the sump on their engine knows it isn't possible on the stock Lotus chassis due to a welded crossmember that goes right below the oil pan.

It's my understanding that on the Spyder chassis that are supplied now, this crossmember is affixed via a bolted connection rather than a weld so that it can be removed for the aforementioned purpose.

So I have a stock Lotus chassis, and my question is this: would it be unsafe if I were to cut off the welded crossmember, grind the old mounting point flush with the chassis, and buy a section of steel U-channel stock that is the same size as the original crossmember and drill holes and bolt it to the chassis?

Basically, can I replace the welded crossmember with a bolted one safely? Assuming of course that I use grade 8 bolts.

Thanks,
Ben
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PostPost by: tvacc » Fri Nov 01, 2019 5:24 pm

What I did in the past, way past, like in the early 70's on my Elan S2 now owned by Jeff K who is a member of this list, is that I cut the channel, then I found two pieces of channel that fit right inside the channel I cut off. I drilled four holes and bolted it back up. Been that way for 45 years. Seems to work just fine. Maybe Jeff can take a picture. I am sure he will read this.
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PostPost by: tvacc » Fri Nov 01, 2019 5:26 pm

Oh, I did not take off the old channel. I just put the new channel inside the old channel and bolted it all back up. I think that is the better way so you don't disturb or drill the frame.
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PostPost by: 69S4 » Fri Nov 01, 2019 6:37 pm

There?s a lot of posts going way back about doing this. I spent 10yrs thinking about it and a couple of days last year doing it. I found some suitable channel that would fit inside the existing piece, drilled holes to bolt the new channel in place as a marker before cutting one side (in case the chassis rails ?sprang?), welded the new channel to the central old piece, bolted the chassis rail side up then repeated the process on the other side. To date (about 3k miles) there has been no difference - exactly as I?d hoped. Payoff will hopefully come when I get round to dropping the sump to fix the oil leaks left over from the last bodged sump refit
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PostPost by: benymazz » Fri Nov 01, 2019 8:05 pm

tvacc wrote:What I did in the past, way past, like in the early 70's on my Elan S2 now owned by Jeff K who is a member of this list, is that I cut the channel, then I found two pieces of channel that fit right inside the channel I cut off. I drilled four holes and bolted it back up. Been that way for 45 years. Seems to work just fine. Maybe Jeff can take a picture. I am sure he will read this.


Just to make sure I am understanding this right - you cut the channel so there was excess sticking off of the chassis rails, and used the new channels to "splice" the cut section to the section still welded to the frame, and only drilled holes in the old U channel and not through the frame itself?

The only thing I would be worried about if I am in fact understanding you right would be the whole thing pivoting around the bolts. It would be fine if the crossmember was in tension but if it got put in compression there's nothing to stop it from pivoting about the bolts and "buckling"?

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PostPost by: Mick6186 » Fri Nov 01, 2019 8:16 pm

Well the crossmember on the +2 is bolted to the chassis so must be OK,
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PostPost by: RichardHawkins » Sun Nov 03, 2019 8:39 pm

Ben,

Like you I was concerned that this cross member might be in compression, but if you look at its proportions it is rather too slender to carry any useful load in compression. I took the advice of another owner who said he had done this years ago and never noticed any problems. Much later, during this summer, I was test fitting my engine and gearbox without the cross member being bolted in place, and noticed that as the chassis took the weight of the engine the bottom flanges of the chassis moved apart. I tried to fit the cross member but could not do so unless I lifted the engine slightly. I consider this to be evidence that the cross member is in tension, not compression and that my concerns about the bolted joint are unfounded.

Hope this helps,

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PostPost by: steve lyle » Sun Nov 03, 2019 10:29 pm

benymazz wrote:
The only thing I would be worried about if I am in fact understanding you right would be the whole thing pivoting around the bolts. It would be fine if the crossmember was in tension but if it got put in compression there's nothing to stop it from pivoting about the bolts and "buckling"?

Ben


If you're worried about compression, use two bolts on each end of the brace.
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PostPost by: cbguerrajr » Mon Nov 04, 2019 4:25 am

I followed the general process described above with my S2 except I used 1"x1" square steel tubing (from Home Depot) which fits inside the existing welded channel. To make sure that the sides of the frame didn't move out, I first attached the tube to the crossmember with C clamps and drilled the holes through the tubing and crossmember at the same time. Then cut the old crossmember leaving about 2-3 inches sticking out. In my car the distance between holes with or with out the crossmember did not change, because the holes still lined up.
A warning, though. The oil pan may still not come out unless you have a split bell housing dust cover. The rear of the oil pan gets hung up with the original one piece dust cover, you can't swing it down enough to clear.
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PostPost by: h20hamelan » Mon Nov 04, 2019 5:21 am

Cutting the welds works well, so does cutting the existing crossmember.
If your concerned about the width of the frame at that point. Use a brace, a 2x4 or suitably strong support. Or measure in advance, and note deflection.
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PostPost by: seriouslylotus » Mon Nov 04, 2019 7:19 am

The new 26r chassis' have a removable cross member.
Drill the holes before removing the welds.
Last edited by seriouslylotus on Mon Nov 04, 2019 8:53 am, edited 1 time in total.
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PostPost by: rgh0 » Mon Nov 04, 2019 8:42 am

RichardHawkins wrote:Ben,

Like you I was concerned that this cross member might be in compression, but if you look at its proportions it is rather too slender to carry any useful load in compression. I took the advice of another owner who said he had done this years ago and never noticed any problems. Much later, during this summer, I was test fitting my engine and gearbox without the cross member being bolted in place, and noticed that as the chassis took the weight of the engine the bottom flanges of the chassis moved apart. I tried to fit the cross member but could not do so unless I lifted the engine slightly. I consider this to be evidence that the cross member is in tension, not compression and that my concerns about the bolted joint are unfounded.

Hope this helps,

Richard Hawkins


I carried out the same tests and found the same things when I made my Elan cross member removable about 40 years ago. Been fine since

cheers
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PostPost by: prezoom » Mon Nov 04, 2019 3:53 pm

My S2 has a removable crossmember, done by the previous owner. It can be bolted up with the engine in place or with the engine out without having to force any part of the chassis rails to get hole alignment. Same goes for my Plus2, which has the factory installed removable crossmember. The crossmember in the Plus2 was not installed when I fabricated the engine mounts for the Zetec, and after installing the engine for the last time, the crossmember slid nicely into place. Either I got lucky, or there is not much movement of the chassis rails with with the engine in or out.
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PostPost by: CBUEB1771 » Mon Nov 04, 2019 7:42 pm

Mick6186 wrote:Well the crossmember on the +2 is bolted to the chassis so must be OK,
Mick


Very true, just keep in mind that on the +2 both the chassis and the cross member have conical features which nest into each other so that the bolts don't take all of the load purely in shear. The weight of the engine puts the cross member in tension which the conical features convert to partly tension and partly shear in the two attachment bolts.
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PostPost by: TomR » Wed Nov 06, 2019 2:36 pm

I have a TTR chassis with removable crossmember. But I chose to substitute a generic adjustable strut brace. I did dimple the frame and used conical washers to distribute the shear as Russ points out.
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